1. Field of the Invention
The present invention relates to a thermistor such as a positive characteristic thermistor (hereinafter referred to as "PTC thermistor") and a negative characteristic thermistor (hereinafter referred to as "NTC thermistor"), and more particularly to an improvement of the thermistor having a structure in which electrodes are formed on the main surfaces of a plate-like thermistor body or element.
2. Description of the Related Art
There has been known a plate-like PTC thermistor 1 the section of which is shown in FIG. 3. The PTC thermistor 1 has such a structure that electrodes 3 and 4 are formed on both the entire surfaces of a disk-shaped thermistor body 2 made of semiconductor ceramic. In the PTC thermistor 1, the electrodes 3 and 4 must be made of material kept in ohmic contact with the thermistor body 2. Further, it is preferable that the electrodes 3 and 4 are made of the material which has the resistivity as low as possible and capable of providing a larger current capacitance.
For this reason, conventionally, the electrodes 3 and 4 were formed in such a manner that Ag or an Ag alloy is applied to the main surfaces of the thermistor body 2 by printing/baking or sputtering.
However, the electrodes 3 and 4 made of Ag or an Ag alloy has a defect that they are likely to migrate therebetween or generate inter-electrode migration. That is, while the thermistor is used, the material of the electrodes 3 and 4 migrates each other towards the electrodes 3 and 4 on the opposite sides so that short-circuiting occurs on the side of the thermistor body 2. In the worst case, the PTC thermistor was broken.